This application claims the priority of German application No. 198 12 170.9, filed Mar. 19, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a fuel injection system for a multi-cylinder internal combustion engine with a cam-controlled high-pressure injection pump for transporting fuel to a common fuel line (common rail), which acts as a high-pressure storage system from which injection lines lead to injection nozzles, and which possesses a solenoid valve control that determines the respective initial point for feeding fuel to the engine.
Such a fuel injection system is disclosed in MTZ Motortechnische Zeitschrift 58 (1997) 10. In this system, costly injectors are used, each of which possesses an injection nozzle, a piston valve, as well as a solenoid valve. In this design, the high fuel pressure acts upon the common fuel line and in the injection lines, and also concurrently acts directly on the pressure absorption area of the injection nozzle and the larger absorption area of the piston valve which delimits a control space through which the injector needle is pressed onto its seat. After the solenoid valve is opened, a decrease of pressure is created at the piston valve, which in turn causes the injector nozzle to open. For completion of the injection process, the solenoid valve is closed, the entire gas pressure once again acts upon the piston valve and the injection nozzle closes again.
If the fuel, which is queued at the injector nozzle or at the injector needle, is injected into the combustion chamber at the beginning of the injection process and under extremely high pressure, then at the time of the beginning of the ignition, the pressure, temperature and also the NO.sub.x formation in the combustion chamber rise very steeply. In order to achieve a nominal NO.sub.x limit, the beginning of the injection has to be shifted in the direction of "late". As a result of this shift, the injected fuel cannot be used efficiently.
It is therefore an object of the invention to provide a fuel injection system, in which a large increase of the fuel pressure at the beginning of the injection process is reduced.
Another objective of the invention is to reduce combustion noise.
These and other objects and advantages are achieved by the fuel injection system according to the present invention, in which the solenoid valve is shifted into close proximity of the area of the common fuel line. As a result, costly injectors can be dispensed with and only one standard injection nozzle is used. Thus, in the simplest manner, a fuel injection system is created in which the increase of the fuel pressure in the exposed injection line at the start of the feeding of fuel to the engine can be delayed due to the long distance between the solenoid valve and the needle seat of the injection nozzle. That is, because of this long distance, with its correspondingly large dead volume, the ignition is delayed, and neither the pressure nor the temperature rise as steeply. While using the same starting point for feeding the fuel to the engine, distinctly less NO.sub.x is produced.
Because the NO.sub.x values are well below the nominal limit, the starting point for feeding fuel to the engine can be greatly advanced (shifted in the direction of "early") until the NO.sub.x values again reach the same limit. However, as a consequence of the earlier starting point for feeding fuel to the engine, the fuel is used more efficiently, which has the benefit of reducing the specific fuel consumption.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.